1. Field
The embodiments discussed herein are related to a communication control method and a transmitting apparatus, which are used in a communication network that converts a transmission format of a data signal and performs communication.
2. Description of the Related Art
A Synchronous Optical NETwork (SONET) (also referred to as a Synchronous Digital Hierarchy (SDH)) has been used as a network interface for realizing Broadband Aspects of Integrated Services Digital Network (B-ISDN).
In a communication network of the SONET or SDH (hereinafter, referred to as SONET/SDH) system, a data signal is transmitted using a data frame (transmission frame) having an overhead portion and a payload portion. The overhead portion has a pointer, for example, that indicates a relative position of a head of a payload (data body) accommodated in the payload portion. As a result, the transmission frame can accommodate the payload using an arbitrary position of the payload portion as the head.
As an existing technique that is related to the SONET/SDH, a method has been known that allows a communication apparatus to monitor reception states of flags sequentially arriving at a predetermined interval through a link fixed between the communication apparatus and a facing apparatus, and determine whether the link is normal or abnormal, thereby quickly determining a link state.
In addition, a method has been known that encrypts data of a transmission packet, encapsulates data including the encrypted data, and transmits the packet, thereby securing a security with a host at the time of communication.
Japanese Patent Application Laid-Open No. 2004-207878 and Japanese Patent Application Laid-Open No. 10-271167 disclose related techniques.
There is a communication network that transmits IP packets between Internet protocol (IP) networks through the communication network of the SONET/SDH system.
For example, in the IP network, IP packets are transmitted with a transmission format using a data frame having a variable length. In addition, in the communication network of the SONET/SDH system, a data signal is transmitted with a transmission format using a continuous byte sequence.
That is, since the transmission format used in the communication network of the SONET/SDH system is different from the transmission format of the IP packet, the IP packet cannot be transmitted as it is in the communication network of the SONET/SDH system.
Accordingly, for example, frames having a variable length are converted (encapsulated) into a continuous byte sequence and transmitted in a SONET/SDH transmitting apparatus at the transmitting side of IP packets, and the frames are decapsulated and the IP packets are extracted in a SONET/SDH transmitting apparatus at the receiving side of the IP packets.
However, during an encapsulating process, a plurality of methods is used. For this reason, if recognitions of encapsulation methods are mismatched in the IP packet transmitting side and the IP packet receiving side, the received transmission data cannot be normally decapsulated at the IP packet receiving side. As a result, transmission efficiency of the communication network may be lowered.